Machine tool



Patented Aug. 18, 1942 UNITED STATES PATENT OFFICE MACHINE TOOL Leo F. Littwin, Chicago, Ill.

Application October 6, 1941, Serial No. 413,821

13 Claims.

My invention relates to machine tools and more particularly to an electric valve circuit for controlling certain operations of such machinetools.

1n machine tools of the type having a reciprocating traveling work-table and a tool-head operable transversely with respect to the worktable, it has been found desirable to provide means for automatically advancing the tool-head each time that the Work-table reciprocates or each time that the work-table moves iny either direction. Heretofore this has been accomplished by an electric circuit which was closed each time that the work-table reciprocated, and was opened by electric contact devicesand relays as the cutting head was advanced a predetermined amount. Such circuits employed electromagnetic relays and a series of electric contacts spaced along the way or the path of travel of the tool-head. It was found that the variations in the times of operation of the relays was sufliciently great to introduce a serious degree of inaccuracy in the operation of the machine-tools, and that furthermore, it Was difficult to maintain the contacts clean so as to prevent delayed operation due to contact resistance. ,In accordance with my invention, a tool-head is advanced at a certain constant rate of travel, and the distance which the tool-head is advanced is determined by controlling the time interval during which the tool-head travels without the use of relays or contacts.

It isy therefore, an object of my invention to provide a new and improved apparatus for controlling the operation of a machine-tool which will overcome the above mentioned disadvantages.

It is another object of my invention to provide an improved arrangement for controlling the position of 4a tool-head on a machine-tool in accordance with the work performed on `the stock supported on the work table.

Still another object of my invention is to provide an improved electric valve circuit for selectively predetermining the time of operation of a device, irrespective of the variations in the intervals between successive operations.

Other and further objects of my invention will become more readily apparent by reference to the following description taken in connection with the accompanying drawing wherein Figure 1 is a perspective view of the essential parts of a machine-tool to which the present invention is applied; and

I Figure 2 is a circuit diagram of the electric valve circuit embodying the present invention. Referring more particularly to Fig. 1, there is shown certain essential elements of a machine tool, and these include a supporting frame 5 upon which a work-table 'B is arranged to travel on horizontal ways. The Work table 6 is actuated by mechanism which may be variable in speed and which can be controlled so as to determine the length of travel of the work-table. Supported toward the rear of the base or frame 5 there are two vertical columns 'I and 8 provided with suitable slides or ways to guide the travel of a tool-head support 9,` which in turn is provided with suitable horizontal slides or ways in which a tool-head II operates. Thus, by means of the vertical slides or ways formed by the columns 'I and 8, the tool head II may be elevated to a desired position above the work-table '6 upon which the stock is supported. In Fig. 1, the tool head II is shown as being a grinding wheel provided with a shield and a lubricating tube, but it is to be understood that this tool head may comprise any other cutting or finishing tool.

In operation, the work-table 6 is moved back and forth between certain limits which may be determined by a pair of adjustable limit stops I2 and I3 supported from a member directly beneath the front edge of the work-table E. 'I'hese limit stops actuate switch levers I4 and I5 which are connected to electrical or mechanical reversing means for driving the Work-table 6. As the stock on the work-table 6 is moved back and forth with respect to the cutting head I I, it is desired to automatically move the tool head II across the stock by small increments of distance. This may be accomplished by any suitable means such as a hydraulic piston I6, .shown in dotted lines, which is supplied with a uid through a pipe II and a valve I8. The valve I8 is opened and closed by a solenoid I9. The solenoid I9 is energized by a suitable electric circuit,

' shownin Fig. 2, which is controlled by a switch noid I9.

Referring more particularly to 2, it will be seen that an electric circuit is provided -which receives alternating current energy from suitable onductors 23 and 24. .Connected between the conductors 23 and 24 are a pair of reversely connected controlled electric valves 25 and 26, which supply energy to a solenoid I9 which is connected to control the'operation of the valve i8. The valves 25 and 26 may comprise any of the controlled electric valves Well known in the art, but for purposes of illustration there is shown a preferred form of electric valve having an anode, a cathode and a control electrode in the form of a capacitor band surrounding the outside of the envelope of the valve at a proper place between the anode and the cathode. It furthermore will be readily appreciated that these valves may have control characteristics corresponding to any one of a diierent number of types of characteristics, but for the purposes of explanation of the circuit, it will be assumed that these valves have control characteristics such that they will become conductive whenever the control electrode is at zero or a slightly positive potential. The solenoid i9 opens the valve i8 thereby to permit the hydraulic cylinder i6 to advance the tool-head il at a certain constant rate. The time interval of the opening of the valve i8 determines the distance which the tool-head is advanced, and this, in turn, is determined by the length. of time of conductivity ofthe valves 25 and 26.

in order to provide definite periods of conductivity for the valves 25 and 26, there is provided a control circuit which includes a rectifier valve 21 and a controlled electric valve 28. Certain potentials for the operation of these valves and for the control electrodes of the electric valves 25 and 26 are obtained from a transformer 29 having a primary winding 3l connected between the conductors 23 and 24. The transformer 29 is provided a plurality of secondary windings, of which the windings 32, 33 and 34 serve to supply heating current to the cathodes of the valves 25, 26 and 2, respectively. A tapped secondary winding 35 is connected across a resistor 36, and one portion of the secondary winding35 supplies cathode heating energy to the cathode of the controlled electric valve 28. The transformer 29 is further provided with secondary windings 3l and 39 which are connected the switch 2|. The switch 2l is of a type which is closed for a relatively short interval of time by the toggle arm or mechanism 22 attached to the limit switch levers I4 and I5.

The controlled electric valve 28 has its cathode connected to the conductor 24, and its anode connected to the juncture between the transformers l5 and 38. The control electrode of the valve 28 is connected to the juncture between a pair oi resistors i9 and 49. A capacitor 5I is connected across the resistors 48 and 49 and this circuit constitutes a resistance capacitance time control in the control circuits of the valves 25 and 26,

respectively. The control circuits of the valves 25 and 26, furthermore, at times include energy supplied from a transformer 39 having a primary winding 4I connected in series with a resistor 42 so as to be energized by the voltage appearing across the solenoid I9 whenever the electric valves 25 and 26 are conductive A capacitor 43 is connected across the primary' winding il of the transformer 39 so as to provide the proper phase relation between the voltage obtained from the solenoid i9 and the voltage to be supplied to the control circuits of the valves 25 and 26. The transformer 39 is provided with secondary windings lili and d5 which are connected in series with the secondary windings 3l and 3S, respectively, of the transformer 29. Thus the control circuit for the electric valve 25 may be traced from the cathode to the conductor 23, through transformer winding 94, transformer winding 31, and a suitable ,current limiting resistor d5 to the control electrode of he valve 25. Similarly the control circuit for th electric valve 26 may be traced from the cathode of the valve through the transformer winding d5, the transformer winding 38, and a suitable current limiting resistor il to the control electrode. The control electrodes of the valves 25 and 26 are connected by suitable conductors to the contacts of circuit which is connected between the anode oi 'l'he electric valves 25 and 26 are :normally` maintained non-conductive by a suitable bias potential supplied by the transformer windings 91 and 38 of the transformer 29. During the periods when these valves 25 and 26 are non-conductive, the only potential supplied to the control electrodes of the valves are the negative bias potentials supplied by the transformer windings 31 and 98. It will be remembered that the control electrodes are connected to the contacts of the switch 2l so that each time that the limit stops i2 and i3 engage the limit switch levers iii and i5, the toggle 22 actuates the switch 2l thereby completing a circuit which may be traced from the cathode of the valve 25 and the conductor 23 through transformer Winding 34, transformer winding 3l, the current limiting resistor e6, the switch 2l, the current limiting resistor 21, the transformer winding 36, the transformer winding 45, to the cathode of the valve 26 and through the solenoid i9 to the other electric conductor 24. ri'hus, the alternating current normally supplied by the transformer windings 31 and 38 is rendered ineiective with respect to the valves 25 and 26 so that during the interval that the switch 2i is closed one of the electric valves 25 or 26 will be rendered conductive dependent upon which half of the alternating current cycle is effective with respect to these reversely connected electric valves. Since one of the electric valves 25 or 26 is rendered conductive, current is supplied to the solenoid I9 which, in turn, opens the valve It` to permit a supply of uid through the pipe I'I to the hydraulic cylinder I 6` thereby to change the position of the tool-head II of the tool-machine. causes an alternating current voltage to be supplied to the circuit comprising the resistor 42 and the transformer winding 4I of the transformer 39. The capacitor 43 determines the phase relation of the alternating current to be supplied by the transformer secondary windings 44 and 35. The secondary windings are arranged to supply a potential of such magnitude and sign as to render ineffective the alternating current potentials supplied by the transformer windings 3T and 38 of thetransformer 29. rlhus the control electrodes of the valves 25 and 26 will be maintained at such potentials as to maintain these valves in a state of conductivity, thereby continuing to supply energy to the solenoid i9. After a predetermined time, the circuit which includes the valves 2l and 28 will operate to again render non-conductive the electric valves 25 and 26.

During the periods when the electric valves 25 and 29 are non-conductive there appears a potential across the electric valve 2l and the resistors t9 and i9 such that the electric valve 2l supplies current to the capacitor 5i thereby to The supply of energy to the solenoid I9' ceeding half cycle.

charge this capacitor. It will be seen that a circuit may be traced from the conductor 23 through the electric Valve 21 and the parallel circuit comprising resistors 48 and 49 and the capacitor 5I through the resistor 36, the transformer 35 and a conductor 53 to the conductor 24. The conductor 53 is connected to the mid-tap of the transformer winding 35. Whenever the electric valves 25 and26 are rendered conductive, the potential across the electric valve 21 drops sufficiently so that the capacitor I begins to discharge through resistors 48 and 49. Ihe controlled electric valve 28 will thereupon become conductive as soon as the potential appearing across the resistor 49 is sufficiently low. 'Ihe time interval between the time when one of the electric valves 25 or 26 becomesconductive and the time when the electric valve 28 is permitted to become conductive may be controlled by adjustment of the contact 52 on the resistor 36 which is connected to the cathode of the valve 28. Whenever the controlled electric valve 28 becomes conductive, the potential supplied by the transformer winding 45 is reduced to such a degree that the control potential supplied by the transformer winding 38 is effective to render nonconductive electric valve 28 on the next suc- The non-conductivity of the electric valve 28 for a half cycle reduces the voltage across the solenoid AISI so that voltage supplied by the transformer 39, which receives its energy from the solenoid I9, will be insufficient to overcome the effect of the negative biasing potential supplied by the transformer 29 and its secondary windings 31 and 38. Thus the electric valve 28 operates to reduce the positive potential supplied-to the control electrode of the valve 26 sufciently to render this valve non-conductive and this, in turn, has the effect of permitting the negative bias in the control circuit of the control electrode of the electric valve 25 to again regain control over the valve 25 thereby also rendering this valve non-conductive.

From an explanation of the operation of the control circuits 25 and 26, it is apparent that the periods of conductivity of the electric valves 25 and 26 may be selectively predetermined thereby to control the time interval for which 'the valve I8 is held in an open position by a solenoid I9.. Thus, where the tool-head is a grinder as shown in Fig. 1, the grinder is moved to a new position each time that the stock on the worktable 8 completely passes the tool-head II. Obviously, of course, where other tools are used in place of the grinder, the control arrangement may be modified so that the switch 2| is actuated only upon the movement of the work-table 5 in a `particular direction rather than actuating the switch 2I upon each direction of movement of the work-table. The arrangement shown and described limits the possibilities of inaccuracies in operation since the control is accurate 4to 1,420 Voi' a second or within the limitation of a half cycle of alternating current. bodiment of a machine of the type shown in Fig. 1, the cutting or tool-head II has been moved by anyv desired increments within an accuracy limit of .0001 of an inch.

While, for the purposes of illustrating and describing the invention, a particular circuit arrangement has been shown as applied to a particular machine-tool, it, of course, is to be underto which the circuit is applied without departing from the spirit and scope of the appended claims.

I claimz.

l. 'I'he combination comprising a source of alternating current, a plurality of controlled electric valves, and a work circuit energized by said valves, a control circuit for each of said valves including a source of potential t0 maintain said valves non-conductive, means for renderingr` ineffective said potentials for an interval suflicient to render conductive one of said valves, means responsive to power flowing through said work circuit for supplying a second control potential to l each circuit to maintain conductive said valves,

Thus in 011e E111-- and means operative after a predetermined time interval after the initiation of conductivity of said valves for rendering ineffective one of said latter potentials thereby to render said valves non-conductive.

2. The combination comprising a source of alternating current, a plurality of controlled electric valves, and a work circuit energized by said valves, a control circuit for each of said valves including a source of potential to maintain said valves non-conductive, means for rendering ineffective said potential for an interval sufficient to render conductive one of said valves, means responsive to power fiowing through said 'work circuit for supplying asecond control potential to each control circuit to maintain conductive said valves, and means operative after a predetermined time interval for reducing only one of said latter potentials sufficiently to render said valves non-conductive.

3. The combination comprising a source of alternating current, a plurality of controlled electric valves, and an output circuit therefor, a control circuit for said valves including a source of potential to bias said valves non-conductive, means' for rendering ineffective said source of bias potential for an interval suflicient to permit one of said valves to become conductive, means connected across said output circuit for supplying a second control potential to overcome the effect of said first potential, means responsive to the conductivity of said rst valves for reducing the effectiveness of said latter potential sufliciently to render one of said valves non-conductive, said means comprising a controlled electric valve connected so as to by-pass said latter po tential, said latter valve being arranged t0 be rendered conductive a predetermined time interval after power begins to flow in said output circuit.

4. The ocmbination'comprising a pair of controlled electric valves and an output circuit en.. ergized from a source of alternating current, a control circuit for each of said valves including a source of'bias potential for maintaining said valves non-conductive, a switch connected to said control circuits for rendering ineffective the bias potential supplied by said sources by connecting said control circuits in series, means energized in response to power flowing 'through said output circuit for supplying to each circuit a second bias potential to overcome the effect of said first bias potential thereby to maintain conductive said valves, and means responsive to the conductivity stood that I do not wish to be limited thereby since obviously modifications may be made in the circuit arrangement and in the instrumentalities connected to be energized by said valves, a control circuit for said valves including a source of alternating current bias potential for maintaining said valves non-conductive, means for rendering ineiective the bias potential from said source for a short time interval thereby to permit one of said valves to become conductive, means energized from power flowing through said output circuit, for supplying an alternating current control potential opposite in sign to said first alternating current bias potential, said means being connected in Tseries with said rst source of potential thereby to maintain conductive both of said valves in response to the conductivity of one of said valves, and means responsive to the conductivity of said rst valves for reducing the magnitude of the potential supplied by said latter means after a predetermined time interval thereby to render both said valves non-conductive.

6. The combination comprising a source of alternating current, a pair of reversely connected controlled electric valves, and a work circuit energized by said valves, a control circuit for said valves including a source of alternating current potential to bias said valves to maintain them non-conductive, means operative for a sh'ort time interval for rendering ineiective said bias potential thereby to permit one of said valves to become conductive, means energized from power flowing through said work circuit for supplying an alternating current control potential of such sign and magnitude as to overcome the effect of said first bias potential thereby to maintain the conductivity of said valves, and means responsive to the conductivity of said valves for reducing the magnitude of said latter potential after a predetermined time interval, said means comprising a controlled electric valve connected so as to reduce the magnitude of said latter potential, said latter valve being provided with means for selectively predetermining the duration of the time interval.

7. In a metal working machine having a reciprocating traveling work-table, a tool-head arranged for movement transverse with respect to said work-table, means for moving said tool-head, the combination for controlling the distance which said tool-head will advance upon each stroke of said work table comprising a source of alternating current, a plurality of reversely connected control electric valves connected thereto, means operated by said electric valves for controlling the actuation of said tool-head, a control circuit for said valves including a source of potential to maintain said valves non-conductive, a switch actuated upon each stroke of saidl worktable for rendering ineiective said potential for an interval suicient to render conductive one of said valves, means responsive to power ilowing through said electric valves for supplying a second control potential opposed to said ilrst control potential to maintain conductive said valves, and means responsive to the initiation of conductivity of said valves for reducing the effectiveness of said latter potential after a predetermined time interval thereby to render said valves non-conductive.

` 8. In a machine tool having-a traveling worktable, a tool-head arranged for movement across said work-table, means for moving said tool-head at a relatively constant rate, a solenoid for controlling said means, th'e combination for selectively predetermining the length of travel oi said tool-head comprising a source of alternating current, a pair of reversely connected controlled elecsource to said solenoid, a control circuit for the control electrodes of said valves including a source of control potential for maintaining said valves non-conductive, a switch actuated by the travel of said work-table and connected to remove from the control electrodes of said valves said potential for an interval suicient to render conductive one of said valves, means responsive to power owing through said solenoid for supplying a second control potential to overcome the effect of said rst control potential thereby to maintain conductive said valves, and means responsive to the initiation of conductivity of one of said valves for reducing the effectiveness of said latter control potential after a predetermined time interval thereby to permit said first control potential to render said valves non-conductive,

9. In a machine-tool having a traveling worktable and a movable tool-head, means for moving said tool-head at a certain rate, the combination for selectively predetermining th'e time interval of travel of said tool-head comprising a source of alternating current, a pair of reversely connected controlled electric valves, means connected in series with said valves` for controlling said toolhead moving means, a control circuit for the control electrodes of said valves including a source of alternating current control potential for maintric valves connected to supply energy from said taining said valves non-conductive, means actuated by said work-table for rendering ineffective said potential for an interval of time sufiicient to render conductive one of said valves, means ener: gized by thevoltage appearing across said mans for controlling said tool-head moving means, said means operating to supply a second alternating current control potential of such sign and magnitude as to maintain conductive said valves, and a selectively controlled time constant circuit operative in response 'to the initiation of conductivity of said valves, and a controlled auxiliary valve having a control electrode energized by said latter circuit, said latter valve being connected to reduce the effect of said second alternating current control potential thereby to render non-conductive both said valves.

l0. The combination comprising a source of alternating current, a plurality cf controlled electric valves, a work circuit energized by said valves, a control circuit for each of said valves including a source of alternating current potential for maintaining said valves non-conductive, means for rendering ineffective said potential for an interval suiiicient to render conductive said valves, means responsive to power ilowing through said work circuit for supplying an alternating current control potential to each circuit to maintain conductive said valves, and means operative after a predetermined time interval after the initiation of conductivity of said valves for rendering ineffective the latter potential thereby to render said valves non-conductive.

11. The combination comprising a source of alternating current, a plurality of controlled electric valves connected to a work circuit, a control circuit for each of said valves including a source of alternating current potential for maintaining said valves non-conductive, means for rendering ineffective said potential for an interval sufficient to lrender conductive said valves, means responsive to power flowing through said work circuit for supplying another alternating current control potential ,to each control circuit to overcome the eect of said lrst alternating current potential thereby to maintain conductive said valves, and means operative after a predetermined time interval after the initiation of conductivity of said valves for reducing said latter potential suiiiciently to render said valves non-conductive.

12. The combination comprising a .source of alternating current, a pair of reversely connected controlled electric valves, and a work circuit y.energized by said valves, a control circuit for said valves including a source of alternating current potential to bias said valves to maintain them non-conductive, means operative for rendering ineiective for a short time interval said bias potential thereby to permit said valves to become conductive, means energized from power ilowing through said work circuit for supplying an alternating current control potential of such sign and magnitude as to overcome the effect of said rst bias potential theneby to maintain the conductivity of said valves, and means responsive to the conductivity of said valves for reducing the magnitude of said latter potential after a predetermined time interval, said means comprising an auxiliary controlled electric valve connected so as to reduce the magnitude of said latter potential, said auxiliary valve having a control circuit for selectively predetermining the duration of said time interval, said circuit including a half-wave rectier connected to charge a capacitor from said first mentioned alternating current source only as long as said rst mentioned valves remain nonconductive, and impedance means connected across said capacitor, a portion of said lmpedance means being connected between the cathode and the control electrode of said auxiliary valve in series with an adjustable means for selectively determining said time interval.

13. 'Ihe combination comprising a source of alternating current, a pair of reversely connected controlled electric valves connected between said source and a work circuit, a control circuit for said valves including a source of alternating current bias potential to maintain said valve non-conductive, means for rendering ineffective for a short time interval said bias potential, means energized from said work circuit for supplying an alternating current control potential of such sign and magnitude as to overcome the effect of said first bias potential thereby to maintain the conductivity of said valves, and means responsive to the initiation of conductivity of said valves for reducing the magnitude of said latter potential after a predetermined time interval, said means comprising an auxiliary controlled electric valve connected so as to reduce the magnitude of said latter potential, and a control circuit for said auxiliary valve for selectively predetermining the duration l of said time interval, said control circuit including a half wave rectifier connected to charge a capacitor from said rst mentioned valves remain non-conductive, and impedance means connected across said capacitor, a portion of said impedance means being connected between the cathode and the control electrode of said auxiliary valve.

LEO F. LITTWIN. 

